added tests for getParallelNode().
Don't prevent mousedown when clicking on preview page content.
preview-to-editor-mapping highlights on hover, scrolls on mousedown.
clear marks when mouse leaves html area of preview
preview-to-editor-mapping hover uses mouseover instead of mouseenter now.
Merge pull request #165 from toolness/issue-164

Highlight relevant HTML code on mouse-over of preview frame content
Merge branch 'gh-pages' into i18n